In recent years, a number of medical devices have been designed which are adapted for compression into a small size to facilitate introduction into a vascular passageway and which are subsequently expandable into contact with the walls of the passageway. These devices include, among others, blood clot filters, which expand and are held in position by engagement with the inner wall of a vein, such as the vena cava. These vena cava filters are generally designed to remain in place permanently. Typically, blood filters are made of metal wire in a configuration designed to fill the cross section of the blood vessel with filter members. Such filters must be radially compressed to fit within a delivery catheter, and these filters include structure to anchor the filter in place within the vena cava, such as elongate diverging anchor members with hooked ends that penetrate the vessel wall and positively prevent longitudinal migration of the filter in either direction within the vessel.
Known systems and methods for delivering a blood filter to a location in a patient's blood vessel are disclosed, such as in U.S. Pat. No. 6,258,026, which is hereby incorporated by reference in its entirety. Typically, a filter delivery catheter is positioned within a patient's blood vessel by threading it through a major vein or artery from a point of access, such as the jugular or femoral veins. Once the distal end of the catheter is in position where the filter is to be delivered, the blood filter is placed in the proximal end of the catheter and pushed through to the distal end by a pusher member, such as a stiff wire. When the filter is pushed out of the distal end of the catheter, the filter members spring radially outward to contact the blood vessel's wall. The hooked ends of the anchor members engage the vessel wall and hold the filter in place.
Known systems and methods for installing blood filters have deficiencies and drawbacks. One such deficiency with known delivery devices makes it difficult to align the filter for implantation because there is no self acting mechanism for centering the delivery catheter.